Explain the following:
(i) PbO2 acts as oxidising agent. Why?
(ii) Carbon has a tendency to form long chain compounds but silicon does not. Why?
Answers
i) Lead has an atomic number of 82 that is it's electronic configuration is [Xe] 4f14 5d10 6s2 6p2. The 6s2 electron has a tendency to participate in the formation of a chemical bonding . That is why lead exists in two oxidation states 2+ and 4+ . The 4+ state is very unstable because there is a huge energy difference between the 6s and 6p electrons . So it is not an easy process to promote the 6s electrons to the 6p sub shell for the formation of +4 oxidation state by lead removing it's 4 electrons because this requires a lot of energy . This is known as inert electron pair effect .
In lead dioxide , lead is having a +4 oxidation state and thus to attain stability , lead gives away two oxygen atoms to form lead monoxide in which lead has a +2 oxidation state . That is why lead dioxide undergoes reduction and oxidizes other substances because we know that removal of oxygen is an example of reduction .That is why it acts as a strong oxidizing agent .
ii)The silicon atom is larger than the carbon atom, its covalent radius is 111 pm carbon is 77 pm which makes it more difficult for silicon to form a tetrahedral arrangement with other atoms. The Si-Si bond is also longer and weaker than the C-C bond.